An autocalibrating model for simulating and measuring net canopy photosynthesis using a standard greenhouse climate computer

Abstract

A model for measuring net canopy photosynthesis in commercial greenhouses is described. The problem of calculating CO 2 fluxes at high ventilation rates with sufficient accuracy with commercially available equipment is discussed, and a solution is suggested, using two cooperating submodels and an autocalibration algorithm. The first is a CO 2-balance model which calculates the canopy photosynthesis as the residual accounting for the other CO 2 fluxes. The model stresses the importance of CO 2 infiltration at low ventilation rates and maintains an experience database of measured photosynthesis rates and related climatic variables. Model 2 is a black-box photosynthesis calculation that simulates the crop's photosynthetic response using temperature, irradiance, and CO 2 concentration as variables Model 2 takes over at higher ventilation rates, when model one cannot function with sufficient accuracy. The autocalibration algorithm uses the experience database from model 1 to tune model 2's performance to actual crop characteristics by performing regression routines once every day. The model was implemented using a previously described standard model interface on a standard climate computer system and allowed hourly monitoring of photosynthesis rates in standard greenhouses.